Directional electric heating panel



June 20, 1967 N. E. HAGER, .JR., ETAL 3,327,093

DIRECTIONAL ELECTRIC HEATING PANEL Filed Aug. 21, 1964 m N E W NATHANIEL E- HAGER, JR-

ATTORNEY United States Patent This invention relates generally to a'directional heating panel and more particularly to a heating panel adapted to emit thermal radiation in a preferred direction. Still more particularly, the invention relates to a heating panel which will direct thermal radiation preferentially in a direction other than that which is normal to the plane of the panel.

It is often desirable to direct thermal radiation in a preferred direction other than normal to'the heating panel which supplies the heat. Forv example, a heating panel designed to be positioned in a ceiling will normally radiate thermal radiation directly downward toward the floor. However, it may sometimes be desirable that the radiation from such a ceiling panel be preferentially directed at a nearby door, wall, or window. Cold windows in particular serve as radiative heat sinks, and they extract heat from the room and from the human body by the radiation process. It is difiicult to throw enough heat against the glass by normal means to overcome this situation without supplying too much heat in other areas. It wouldtherefore be desirable to have available a ceiling panel which can preferentially direct heat against such a cold window without overheating the area directly beneath the heating panel.

It is a primary object of the present invention to supply such a panel. It is another object of the present invention to describe a heating panel which will radiate heat in a preferred, predetermined direction to heat various objects which are'positioned along a line whichis not normal to the plane of the heatingsurface.

These objects are accomplished in a surprisingly effective and straightforwardmanner. The invention contem plates the heating panel comprising a supporting sheet having a plurality of grooves therein."Each groove is generallyV-shaped in which the adjacent sides of each groove form an angle at the bottom ofthe V greater than 45 degrees and less than 180 degrees. A plurality of elongated resistance heating elements in the form of metallic foil strips having an emissivity greater than about 0.85 are positioned on corresponding sides of the grooves. On the adjacent side of each groove which has a heating element therein is positioned a reflecting element having an emissivity less than about 0.3.

The supporting sheet on which the heating elements and reflecting elements are to be positioned may be of any convenient material. The sheet or panel may be of wood, plastic, paper laminate, ceramic, metal, or other convenient material. If the material is electrically conductive, then the heating elements to be positioned on the supporting sheet must be electrically insulated from the supporting sheet itself. Such insulation will be the electrical insulation known in the art such as varnishes, papers, glass fiber sheets, and the like. If the supporting sheet material is heat conductive, it is preferred that each heating element be thermally insulated from the supporting sheet in order to minimize heat loss through to the back of the sheet.

Grooves are to be cut in the supporting sheet to provide a sawtooth arrangement in the sheet in cross section. The V-shaped grooves are cut into one side only of the supporting sheet, leaving the other side flat or plane. Each groove is triangular shaped, adjacent sides coming to a point in the sheet, the open side of the triangle 3,327,093 Patented June 20, 1967 coinciding with the position of the surface of the sheet before the grooves were cut therein. Although it is generally contemplated that the supporting sheet shall be flat, the sheet may if desirable be made flexible or in a particular configuration. In suchcases each heating element emits thermal radiation in a direction other than normal to the back of the supporting sheet immediately adjacent the heating element. The supporting sheet with its ridged surface texture may be utilized as decorative elements in ceilings and in walls, and even in such movable fixtures as a door. The supporting sheets may be of any conconvenient size depending on the heat output required of the particular application. The sheets may be in the form of panels, rectangles, or any desired geometrical or irregular or artistic shapes.

The elongated resistance heating elements will be strips I of foil which conduct electricity. The strips may vary in width from about inch up to about one inch, with one-half inch being the prferred width. The strips may readily be cut from the metallic conductive foils available on the market. The metal foil may be aluminum, copper, stainless steel, or any suitable alloy. The thickness of these foils will be generally-in the range of 0.0001- 0.002 inch. Copper foil having a thickness of 0.0008 inch is preferred in view of its low cost, its low heat capacity per unit area, its excellent electrical properties, and its easy workability. Each heating element strip will be positioned on one side of the V-shaped groove cut in one face of the supporting sheet. These V-shaped grooves will generally run parallel to one another and thus the heating strip will be positioned on-corresponding sides of adjacent V-shaped grooves, although not all the grooves need carry a heating element. Since each heating element is designed to emitthermal radiation, its surface should have a high emissivity, higher than about 0.85, and preferably around 0.95. Heaters having low emissivities on their surfaces are ineflicient as radiators. Each heating element should be so adapted that electrical current may be passed down the length thereof. The current and voltages to be used will be selected in accord ance with the resistance of a particular heating element in accordance with Ohms law and in accordance with the requirements of the particular heating application. These features are well understood and will not be described here. Alternating current or direct current may be used, and the heating elements may be connected in series or in parallel as desired. Each heating strip may, if desired, have an extra tab thereon or other feature particularly suitable for making electrical connections to the foil. Each triangular or V-shaped groove which carries a heating element must also carry a reflecting element on the side of the groove facing the heating element. The purpose of this reflecting element is .to reflect thermal radiation in the desired direction and to minimize absorp tion of thermal radiation in the supporting sheet structure. The emissivity of the surface of the reflecting element should be less than about 0.3, and more preferably less than about 0.2 A shiny aluminum foil strip having a width equal to the side of the V-shaped groove on which it is positioned is the preferred embodiment here. Other shiny surfaces such as polished stainless steel, polished steel, and other low emissivity surfaces will suflice. It must be emphasized that most coated surfaces, such as a coating of aluminum paint which appears shiny, nevertheless have higher emissivities and are thus not suitable to serve as the reflecting element in this invention. Although the low emissivity of the reflecting elements to be used herein generally renders unnecessary the use of thermal insulation under the reflecting element in any application, it is conceivable, particularly in the higher temperature applications, that additional thermal insulation underneath 3 the reflecting elements might be needed. The reflecting elements should be electrically insulated from the heating elements. This may most conveniently be accomplished by a coating of suitable temperature-resistant lacquer on the heating element.

The invention will be better understood in reference to the attached drawing in which FIG. 1 shows a simplified isometric view of a heating panel of the present invention,

FIG. 2 shows an enlarged portion of a directional heating panel,

' FIG. 3 shows an alternate configuration of the heating panel, and

FIG. 4 shows a cross-sectional view of the heating panel taken along the lines 4-4 of FIG. 3.

Like elements in the drawing have the same number. Referring particularly to FIG. 1, the supporting sheet 1 has a plane back surface 2 and grooves 3 on the face opposite the back 2. Heating elements 4 are positioned in corresponding sides of the adjacent grooves 3. The reflecting elements 5 are positioned in each groove 3 on the side adjacent the heating element 4. Electrical leads 6 connect opposite ends of the heating element 4 to a source of power 7 by means of which electrical current may be passed down the length of each heating element 4 in order to generate heat by electrical resistance. If desired, an electrical connector 8 may be utilized on one or more of each electrical heating element 4. Although FIG. 1 shows that the heating elements 4. are connected in a parallel configuration, a series circuit may be used if desired.

FIG. 2 shows the wood supporting sheet 1, the heating element 4, and the reflecting element 5. The angle 9 formed by adjacent sides of the V-shaped groove 3 is about 60 degrees in FIG. 2. This angle may vary between 45 degrees and 180 degrees, but will preferably be between 60 degrees and 90 degrees.

FIG. 3 and FIG. 4 show a directional heating panel of the present invention in which the grooves are concentric. Such a panel concentrates heat generally along a line normal to the center of the circular configuration provided the heating elements face toward the center. Alternatively, such a panel may preferably emit radiation away from a line normal to the center of the plane of the circular heater when the heating elements are positioned in the direction facing away from the center.

In some cases convection effects are significant, and only a part of the total heat generated by the panel is radiated. Even then that heat which is radiated is directed in the directional manner described. It has been found that the convection effect can be reduced relative to the radiation effect, or the radiation efliciency can be increased, by covering the panel with a sheet transparent to thermal radiation. The, directional character of the radiation from the panel is not altered if the sheet is sufiiciently transparent. As an example of such a sheet, very thin polyethylene, on the order of one-half mil, may be used as shown in 'FIG. 4 at 10. Strong absorbers of the infra red, such as Mylar film, drastically reduce the directional character of the radiation from the covered panel. Such films absorb the radiation and re-radiate it as a plane surface without directional preference.

I claim:

1. A heating panel adapted to emit thermal radiation in a preferred direction comprising a supporting sheet having a plurality of .grooves therein, each groove being generally V-shaped in which the adjacent sides of each groove form an angle at the bottom of the V greater than 45 degrees and less than 180 degrees, a plurality of elongated resistance heating elements electrically insulated from said supporting sheet and in the form of flat metallic foil strips having an emissivity greater than about 0.85 and positioned on corresponding sides of said grooves, each of said flat metallic foil strips being positioned in face-to-face contact with and covering substantially the entire surface of one side of a respective one of said grooves, a plurality of reflecting elements having an emissivity less than about 0.3 positioned in said grooves adjacent to said heating elements, each of said reflecting elements comprising a fiat metallic foil strip positioned in face-to-face contact with and covering substantially the entire. surface of the other side of a respective one of said grooves, and terminal means on said heating elements for connecting said elements to a source of electric power.

2. A panel according to claim 1 wherein the angle at the bottom of the grooves is in the range -90 degrees.

3. A panel according to claim 1 in which said heating elements comprise copper foil.

4.. A panel according to claim 1 in which said heating elements comprise a stainless steel foil.

5. A heating panel according to claim 1' in which said reflecting element comprises aluminum foil.

6. A heating panel according to claim 1 in which said heating element has an emissivity of about 0.95.

7. A heating panel according to claim 1 in which said grooves are linear.

8. A heating panel according to claim 1 in which said grooves are circular.

9. A heating panel according to claim 1 in which said grooves are covered with a sheet transparent to thermal radiation.

References Cited UNITED STATES PATENTS h 1,494,654 5/ 1924 Weir 219367 1,614,321 1/1927 Smalley 13-25 2,051,637 8/1936 Goldbert et al. 219-461 X 2,139,201 12/ 1938 Nordstrom 1325 2,490,602 12/ 1949 Schick 219-467 X 2,545,805 3/1951 Callender 219-645 2,682,596 6/ 1954 Cox et al 338 -314 X FOREIGN PATENTS 344,972 10/ 1955 Switzerland.

ANTHONY BARTIS, Primary Examiner. 

1. A HEATING PANEL ADAPTED TO EMIT THERMAL RADIATION IN A PREFERRED DIRECTION COMPRISING A SUPPORTING SHEET HAVING A PLURALITY OF GROOVES THEREIN, EACH GROOVE BEING GENERALLY V-SHAPED IN WHICH THE ADJACENT SIDES OF EACH GROOVE FORM AN ANGLE TO THE BOTTOM OF THE V GREATER THAN 45 DEGREES AND LESS THAN 180 DEGREES, A PLURALITY OF ELONGATED RESISTANCE HEATING ELEMENTS ELECTRICALLY INSULATED FROM SAID SUPPORTING SHEET AND IN THE FORM OF FLAT METALLIC FOIL STRIPS HAVING AN EMISSIVITY GREATER THAN ABOUT 0.85 AND POSITIONED ON CORRESPONDING SIDES OF SAID GROOVES, EACH OF SAID FLAT METALLIC FOIL STRIPS BEING POSITIONED IN FACE-TO-FACE CONTACT WITH AND COVERING SUBSTANTIALLY THE ENTIRE SURFACE OF ONE SIDE OF A RESPECTIVE ONE OF SAID GROOVES, A PLURALILTY OF REFLECTING ELEMENTS HAVING AN EMISSIVITY LESS THAN ABOUT 0.3 POSITIONED IN SAID GROOVES ADJACENT TO SAID HEATING ELEMENTS, EACH OF SAID REFLECTING ELEMENTS COMPRISING A FLAT METALLIC FOIL STRIP POSITIONED IN FACE-TO-FACE CONTACT WITH AND COVERING SUBSTANTIALLY THE ENTIRE SURFACE OF THE OTHER SIDE OF A RESPECTIVE ONE OF SAID GROOVES, AND TERMINAL MEANS ON SAID HEATING ELEMENTS FOR CONNECTING SAID ELEMENTS TO A SOURCE OF ELECTRIC POWER. 